Gas generating agent, process for production thereof, and gas generator for air bags

ABSTRACT

There is provided a tubular molded article of a gas generating agent consisting of a non-azide-based composition. Both ends of the molded article are squashed. A gas-generating-agent producing process is to obtain a gas generating agent which is molded into the form of a tube both ends of which are squashed in such a way that the tubular molded article of the gas generating agent being in a wetted state is passed through a gap between a pair of molding gears that are rotatable so that each convex tooth of one of the molding gears can face that of the other molding gear, thereafter the molded article is squashed with the convex teeth at predetermined intervals, thereafter the molded article is cut off at the squashed concave parts in such a way as to be folded, and the resultant cut pieces are dried.

TECHNICAL FIELD

This invention relates to a gas generating agent that generates gaseouscomponents by being burnt to inflate an air bag, a process for producingthe gas generating agent, and an air-bag gas generator that uses the gasgenerating agent.

BACKGROUND ART

Generally, a gas generating composition used in a vehicular safetydevice contains fuel components and oxidizing agents. For example,phase-stabilized ammonium nitrate is used as an oxidizing agent, andtriaminoguanidine nitrate (hereinafter, referred to simply as TAGN) anda combination of TAGN and guanidine nitrate are used as fuel components(see Patent Document 1: U.S. Pat. No. 5,783,773, for example). There isalso a composition in which guanidine nitrate/nitroguanidine is used asa fuel component and in which perchlorate is used as a main substance ofan oxidizing agent (see Patent Document 2: U.S. Pat. No. 5,780,768, forexample). These compositions are to obtain a preferred combustion rateby combining a component having high reactivity, such as TAGN orperchlorate, with an oxidizing agent and a fuel each of which hasinherently low reactivity. However, since the amount of heat generatedby the combustion of the compositions rises on the other hand, thesegas-generating agents are hardly suitable for a gas generator. There isalso a compound being used as a fuel and containing oxygen atoms of 25%or more in an atomic weight ratio in the molecule, and is a combinationof a metallic oxide and a plural metallic oxide (i.e., an oxide having aplurality of kinds of metallic components) (see Patent Document 3:Japanese Published Unexamined Patent Application No. 2000-86375, forexample). Although the combustion temperature is designed to be low inthis composition, the number of gas-generating moles is unsatisfactorybecause the metallic oxides are used as oxidizing agents. If the numberof moles of a gas generated necessary to inflate an air bag is intendedto be secured, the amount of gas-generating agents to be used willincrease, and, as a result, the amount of heat generated by thecombustion of the gas generating agents will increase. In other words,since a large amount of coolant is needed in the gas generator usingthese compositions, it is difficult to achieve a reduction in size andweight of the gas generator.

A molded article of a gas generating agent that can exhibit a highcombustion performance even if its heat value is controlled to be low isshown to solve the above-mentioned problem (see Patent Document 4:Japanese Published Unexamined Patent Application No. H10-87390, forexample). This molded article is produced by molding a gas generatingagent to be shaped like a cylindrical tube, and is burnt simultaneouslyfrom the outer surface of the gas generating agent and from the innersurface of the through-hole so as to burn the agent with highefficiency, and hence is capable of exhibiting a high combustionperformance while restricting the amount of heat generated by itscombustion. As a result, this publication (Patent Document 4) assertsthat a gas generator can be reduced in size and weight. There are alsoPatent Document 5 (Japanese Published Unexamined Patent Application No.2000-239092) and Patent Document 6 (Japanese Published Unexamined PatentApplication No. 2000-319086), each disclosing a molded article of a gasgenerating agent that has a recessed portion on the surface thereof.

Generally, a gas generating agent used in a gas generator for air bagsis required to instantaneously inflate and expand an air bag when acollision or a similar accident occurs. In this respect, the gasgenerator that uses a molded article of a gas generating agent that isdisclosed in Patent Document 4 (Japanese Published Unexamined PatentApplication No. H10-87390) can exhibit a high combustion performance,and therefore can instantaneously inflate and expand an air bag.However, there is a fear that the air bag will adversely affectpassengers because of the inflating shock of the air bag when the airbag is rapidly inflated at the beginning of the expansion thereof. Ifso, the air bag may be incapable of fulfilling its function as a deviceused to ensure the safety of vehicle occupants. Therefore, an ideal gasgenerating agent used in an air-bag gas generator is regarded asgradually inflating an air bag at the beginning of its expansion andthen rapidly inflating it. In other words, a gas generating agent bywhich the pressure in a gas generator varies like the letter S with thepassage of time is required as a gas generating agent capable ofimproving the safety of passengers.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a gas generatingagent, which is formed with non-azide-based compositions, whichrestricts its heat value, which exhibits a high combustion performance,and which is gradually burnt at the beginning of combustion and thenrapidly burnt, provide a process for producing the gas generating agent,and provide an air-bag gas generator that uses the gas generating agent.

In order to solve the above-mentioned problems, the present inventorshave carried out diligent investigations into such a gas generatingagent, a process for producing the agent, and an air-bag gas generatorusing the agent, and, as a result, have achieved completion of thepresent invention.

In more detail, the present invention is a gas generating agent whereina tubular molded article of the gas generating agent is formed withnon-azide-based compositions and in that both ends thereof are molded tobe squashed. Additionally, the present invention is an air-bag gasgenerator that uses the gas generating agent.

Since the gas generating agent of the present invention is molded so asto squash both ends thereof, both ends thereof are first ignited and aremildly burnt at the beginning of combustion. After that, the gasgenerating agent can be rapidly burnt simultaneously from the outersurface of the tube portion and from the inner surface of the inside ofthe tube portion. Therefore, the gas generating agent is suitable to beused in a gas generator for air bags.

A gas-generating-agent producing process of the present invention is toobtain a gas generating agent which is molded into the form of a tubeboth ends of which are squashed in such a way that the tubular moldedarticle of the gas generating agent being in a wetted state is passedthrough a space between a pair of molding gears that are rotatable sothat each convex tooth of one of the molding gears can face that of theother molding gear, thereafter the molded article is squashed with theconvex teeth at predetermined intervals, thereafter the molded articleis bent and cut at the squashed concave parts, and the resultant cutpieces are dried.

Another gas-generating-agent producing process of the present inventionis to obtain a gas generating agent in such a way that the tubularmolded article of the gas generating agent being in a wetted state ispassed through a space between a pair of molding gears that arerotatable so that each convex tooth of one of the molding gears can facethat of the other molding gear, thereafter the molded article issquashed with the convex teeth at predetermined intervals, and themolded article is dried and cut off. Preferably, in this process, bothends of the molded article are squashed. Preferably, the molded articleis cut while being bent at the squashed concave parts, and is sifted.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a main part of an apparatus for producinga gas generating agent according to the present invention.

FIG. 2(a) is an enlarged front view of a molding gear of the apparatusof FIG. 1.

FIG. 2(b) is an enlarged side view of the molding gear of the apparatusof FIG. 1.

FIG. 3 is an enlarged view of an “A” part shown in FIG. 2(a).

FIG. 4 is a view for explaining a situation in which the gas generatingagent according to the present invention is molded.

FIG. 5 shows an example of the gas generating agent according to thepresent invention.

FIG. 6 shows results of a tank combustion test of the gas generatingagent according to the present invention.

FIG. 7 is a table that shows test conditions and results of the tankcombustion test of the gas generating agent according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

This embodiment is concerned with a gas generating agent characterizedby being a tubular molded article of the gas generating agent formedwith non-azide-based compositions and being molded in a state in whichboth ends of the tubular molded article are squashed.

In this embodiment, a non-azide-based composition is normally composedof a nitrogen-containing organic compound, an oxidizing agent, a slagforming agent, and a binder.

In this embodiment, a “molded article” means an element that has beenprocessed to have a predetermined shape by using a mold. An extrusionmolding material is put into a mold formed between an outer diameter andan inner diameter and is extruded therefrom. The extrusion moldingmaterial is then put into a mold formed by convex parts of gears thatface each other so that a molded article has concave parts.

In this embodiment, the outer diameter D of the above-mentioned moldedarticle is preferably from 1.4 mm to 4 mm, the length L thereof ispreferably from 1.5 mm to 8 mm, and the inner diameter d of the insideof the molded article is preferably from 0.3 mm to 1.2 mm. Morepreferably, the outer diameter D of the molded article is from 1.5 mm to3.5 mm, the length L thereof is from 2 mm to 6 mm, and the innerdiameter d of the inside of the molded article is from 0.5 mm to 1.2 mm.Even if a gas generating agent is molded so as to squash both endsthereof, the gas generating agent can have a combustion rate similar tothat of the conventional hollow gas generating agent not having bothsquashed ends (see Patent Document 4: Japanese Published UnexaminedPatent Application No. H10-87390).

A state in which both ends of a molded article of a gas generating agentare squashed means a state in which openings at both ends of the moldedarticle are squashed by two forces applied from the outside to theinside. It is permissible that the openings are either in a state ofbeing completely closed or in a state of being not completely closed.

Preferably, in this embodiment, the gas generating agent is prepared sothat a tank maximum pressure P (kPa) is from 50 kPa to 700 kPa in a tankcombustion test conducted in examples described later. More preferably,the tank maximum pressure P (kPa) is from 50 kPa to 500 kPa.

Preferably, in this embodiment, the gas generating agent is prepared sothat time T (ms) taken from the start-up of a tank pressure to itsarrival at a tank maximum pressure P (kPa) is from 20 ms to 100 ms in atank combustion test conducted in examples described later, and apressure-time curve is traced like the letter S.

Generally, a nitrogen-containing organic compound usable as a fuel for agas generating agent used in an air-bag gas generator, such as one kindor two or more kinds selected from the group consisting of tetrazolederivatives, guanidine derivatives, triazole derivatives,azodicarbonamide derivatives, and hydrazine derivatives, can be used asthe nitrogen-containing organic compound used in this embodiment. Forexample, tetrazole, 5-aminotetrazole, and 5,5′-bi-1H-tetrazole can bementioned as the tetrazole derivatives. For example, guanidine,nitroguanidine, cyanoguanidine, guanidine nitrate, and guanidinecarbonate can be mentioned as the guanidine derivatives. The content ofa nitrogen-containing organic compound in a gas generating compositiondepends on the type of oxidizing agent, the type of additive, or theoxygen balance, and is preferably from 32.5% by weight to 60% by weight.In order to adjust the amount of heat per 1 mol of a gas generated bythe combustion of the gas generating composition to be below 125 kJ,preferably below 115 kJ, and in order to adjust the number of moles fora gas generated to be above 2.70 moles per 100 grams, it is preferableto use one kind selected from the group consisting of guanidine nitrate,nitroguanidine, and 5-aminotetrazole as the nitrogen-containing organiccompound. Especially, guanidine nitrate is relatively low in cost, andhas a melting point higher than 200° C., and hence is extremely stablefrom a thermal point of view. Additionally, guanidine nitrate isexcellent from the point of view of environmental resistance, thus beingsuitable for a gas generating agent. Additionally, since these compoundshave oxygen atoms in the molecule and do not need to have a large amountof oxidizing agents for perfect combustion, a high number of molesgenerated can be expected. Additionally, these compounds have a highnegative standard enthalpy change of formation ΔHf, and, as a result,the amount of energy released during the combustion of the gasgenerating composition is small. Therefore, the combustion temperatureof the gaseous compounds can be controlled to be low.

The 50% mean particle diameter of the nitrogen-containing organiccompound is preferably from 5 μm to 80 μm, and more preferably from 10μm to 50 μm because, if the diameter is too large, the strength willbecome low when a molded article of the gas generating agent is formedtherewith, and, if the diameter is too small, high costs will be neededto crush the molded article. In this description, the “50% mean particlediameter” means the mean particle diameter of 50% based on the numberthereof.

Generally, an oxidizing agent usable for a gas generating agent used inan air-bag gas generator can be used as the oxidizing agent used in thisembodiment. The content of the oxidizing agent in a gas generatingcomposition in this embodiment depends on the type ofnitrogen-containing organic compound, the type of additive, or theoxygen balance, and is preferably from 35% by weight to 65% by weight.In order to adjust the amount of heat per 1 mol of a gas generated bycombustion of the gas generating composition to be below 125 kJ,preferably below 115 kJ, and in order to adjust the number of moles fora gas generated to be above 2.70 moles per 100 grams, it is preferableto, as the oxidizing agent, use one or more kinds selected from thegroup consisting of phase-stabilized ammonium nitrate; ammoniumperchlorate; basic metal nitrate; any one of alkali metal nitrate,alkali metal perchlorate, and alkali metal chlorate; and any one ofalkali earth metal nitrate, alkali earth metal perchlorate, and alkaliearth metal chlorate. From the point of view of easiness in performanceadjustment, it is particularly preferable to use a mixed oxidizing agentobtained by mixing two or more kinds selected from the above-mentionedgroup together. Phase-stabilized ammonium nitrate will be describedhere. Ammonium nitrate is inferior in thermal stability, and causes avolumetric change due to phase transition depending on the temperature.Especially, phase transition occurring at about 32° C. is large involumetric change. Therefore, there is a fear that the strength of thegas generating agent will be lowered, and fire behavior will vary if anexcess and fall from this temperature is repeatedly performed. In orderto overcome this fear, about a 10% potassium salt (for example,potassium nitrate) that contains oxygen atoms is added and mixed toprevent the phase transition. This is called “phase-stabilized ammoniumnitrate.” Basic copper nitrate and the like can be mentioned as a basicmetal nitrate. Sodium nitrate, potassium nitrate, strontium nitrate,etc., can be mentioned as an alkali metal nitrate. Sodium perchlorate,potassium perchlorate, strontium perchlorate, etc., can be mentioned asan alkali metal perchlorate. Sodium chlorate, potassium chlorate,strontium chlorate, etc., can be mentioned as an alkali metal chlorate.Magnesium nitrate, calcium nitrate, barium nitrate, etc., can bementioned as an alkali earth metal nitrate. Magnesium perchlorate,calcium perchlorate, barium perchlorate, etc., can be mentioned as analkali earth metal perchlorate. Magnesium chlorate, calcium chlorate,barium chlorate, etc., can be mentioned as an alkali earth metalchlorate.

Preferably, a mixed oxidizing agent contains one or more kinds selectedfrom the group consisting of strontium nitrate, basic copper nitrate,and phase-stabilized ammonium nitrate, in order to exclude a solidcomponent of a gas generated so as to improve combustibility when themixed oxidizing agent is used as an oxidizing agent. Further, it ispreferable to prepare the mixed oxidizing agent from two or three kindsselected from the group consisting of strontium nitrate, basic coppernitrate, and phase-stabilized ammonium nitrate. A more appropriatecombustion rate can be obtained as a gas generating agent by using thestrontium nitrate for a part of the mixed oxidizing agent. A combustionresidue of strontium nitrate can be turned into an easily filtratedproduct by undergoing a slag forming reaction to a silicon-containingcompound (for example, silicon carbide, silicon dioxide, silicate, orsilane compounds) or to metallic oxide (for example, iron oxide), sothat a solid component in a gas generation can be excluded.

Likewise, it is preferable to allow the mixed oxidizing agent to containat least one kind selected from the group consisting of a basic coppernitrate, alkali earth metal nitrate, and phase-stabilized ammoniumnitrate.

If basic copper nitrate is used as part of the mixed oxidizing agent,the ignitability of the gas generating composition can be improved.Generally, a gas generating agent is ignited by an ignitor and a primingcharge. A gas generating agent inferior in ignitability necessarilyresults in the use of a large amount of priming charges that have alarge heat value, and the gross heat value for each gas generatorincreases. Therefore, the gas generator cannot be reduced in size andweight. Furthermore, a combustion residue produced when basic coppernitrate is burnt is a molten Cu₂O (melting point: 1232° C.)/Cu (meltingpoint: 1083° C.) mist, but is a compound having a high melting point.Therefore, the combustion residue can be easily removed by a coolingmember of the gas generator. The combustion residue can be more easilyremoved by coexisting with the slag forming reaction of strontiumnitrate described later. Also in this respect, the use of the mixedoxidizing agent is effective.

Additionally, it is extremely useful to use phase-stabilized ammoniumnitrate for part of the mixed oxidizing agent. The reason is that theuse of phase-stabilized ammonium nitrate is effective in raising thenumber of moles of a gas generated and in raising the combustion rate.

The type that uses phase-stabilized ammonium nitrate brings danger inproduction by being combined with a highly reactive component such asTAGN disclosed in Patent Document 1 (U.S. Pat. No. 5,783,773).Therefore, it is preferable to use nitrogen-containing organic compoundsother than TAGN when phase-stabilized ammonium nitrate is used, but acombination of TAGN and phase-stabilized ammonium nitrate can be used asa safe gas generating composition, depending on the other oxidizingagents, the other nitrogen-containing organic compounds, or an additiveto be used.

A method for stabilizing the phase of phase-stabilized ammonium nitrateusable in this embodiment is not limited to a specific one, and a methodfor adding a potassium salt to ammonium nitrate can be mentioned as awell-known technique. In this embodiment, a small amount of potassiumperchlorate, a small amount of potassium nitrate, a small amount ofpotassium chlorate, a small amount of potassium nitrite, a small amountof potassium sulfate, a small amount of potassium chloride, and a smallamount of potassium oxalate are added to potassium nitrate, and are thenadded to ammonium nitrate. As a result, ammonium nitrate whose phase hasbeen stabilized is preferable. Ammonium nitrate whose phase isstabilized by potassium perchlorate or potassium nitrate is particularlypreferable from the point of view of thermal stability, oxidizability,etc. The amount of addition of these potassium salts to ammonium nitrateis from 1% by weight to 30% by weight, more preferably from 1% by weightto 15% by weight. A metal complex, such as a diammine metal complex, canbe used as a phase stabilizing agent. If the diammine metal complex isused, desirable metallic components are copper, nickel, and zinc.

The amount of phase-stabilized ammonium nitrate used as a mixedoxidizing agent that is contained in a gas generating composition ispreferably from 35% by weight to 65% by weight, depending on anitrogen-containing organic compound, on the kind of additive, or onoxygen balance. If ammonium nitrate whose phase is stabilized by use ofa potassium salt is used, potassium oxide, potassium carbonate, orpotassium chloride, each having a low melting point and a low boilingpoint, is generated resulting from the combustion of a gas generatingagent. These compounds have an extreme difficulty in being filtratedwith a filter disposed in a gas generator, and there is a fear thatthese compounds will flow out from the gas generator to the outside soas to damage a bag, and hence it is preferable to design the amount ofphase-stabilized ammonium nitrate contained in a gas generatingcomposition to fall within the above-mentioned range.

If the mean particle diameter of the oxidizing agent is too large, thestrength will be lowered when a molded article of the gas generatingagent is formed, and, if the diameter is too small, great costs will beneeded to crush the molded article. Therefore, the 50% mean particlediameter thereof is preferably from 5 μm to 80 μm, more preferably from10 μm to 50 μm.

Generally, a slag forming agent usable as an additive for a gasgenerating agent used in the air-bag gas generator can be used as theslag forming agent used in this embodiment. For example, clay mineral(for example, acid clay, kaolin, or talc), silicon nitride, siliconcarbide, silicon dioxide, silicate, silica, silane compounds, etc., canbe mentioned as concrete examples. In this embodiment, it is preferableto employ a clay mineral or a silane compound.

In the present invention, clay mineral usable as a slag forming agent iscomposed chiefly of aluminum silicate. Aluminum silicate is an inorganicsilicon compound, which has the structure of xAl₂O₃.ySiO₂.zH₂O. Claymineral known as acid clay, or the like, is preferred. The amount ofacid clay contained in the gas generating composition of the presentinvention is normally from 0.1% by weight to 15% by weight, preferablyfrom 0.5% by weight to 10% by weight, more preferably from 0.5% byweight to 8% by weight. If the amount of acid clay contained thereinexceeds this range, the heat value of the gas generating agent willincrease, and hence there exists the possibility that the object of thepresent invention cannot be achieved. If the amount thereof is belowthis range, a combustion residue produced from the burning reaction ofstrontium nitrate will be made fine. Therefore, the combustion residuecannot be caught by the filter of the gas generator, and there arisesthe fear that the residue will flow out from the gas generator so as todamage a bag or the like, and hence there exists the possibility thatthe object of the present invention cannot be achieved. The combustionresidue produced from the burning reaction of strontium nitrate ischanged into a compound that can be easily filtrated with the filter ofthe gas generator by allowing acid clay to be contained in the gasgenerating composition of the present invention. Additionally, thecontaining of acid clay is effective in ensuring the strength of amolded article and in raising a combustion rate.

The silane compound usable as a slag forming agent in this embodiment isan organosilicon compound, and it is preferable to use a silane compoundknown as a silane coupling agent such as vinylsilane, epoxysilane,acrylsilane, or aminosilane. The amount of the silane compound containedin the gas generating composition of this embodiment is normally from0.1% by weight to 15% by weight, preferably from 0.5% by weight to 10%by weight, more preferably from 0.5% by weight to 8% by weight. If theamount of the silane compound contained therein exceeds this range, thecombustion temperature will rise, and there is a fear that nitrogenoxides that bring harm to a person will be produced. Furthermore, sincethe heat value of the gas generating agent is raised, there exists thepossibility that the object of this embodiment cannot be achieved. Bycontaining the silane coupling agent in the gas generating compositionof this embodiment, a combustion residue produced from the burningreaction of strontium nitrate is changed into a compound that can beeasily filtrated with the filter of the gas generator. Additionally, thecontaining of the silane coupling agent is effective in securing thestrength of a resulting molded article and in raising the combustionrate.

Generally, a binder usable as an additive for the gas generating agentused in the air-bag gas generator can be used as a binder usable in thisembodiment. For example, synthetic hydrotalcite, acid clay, talc,bentonite, diatom earth, molybdenum disulfide, crystalline cellulose,graphite, magnesium stearate, and calcium stearate can be mentioned asspecific binders. Additionally, sodium salts of carboxymethyl cellulose,methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,hydroxypropyl methylcellulose, polyvinyl alcohol, guar gum, polyvinylpyrrolidone, polyacrylamide, and a mixture of these compounds canbe mentioned as specific binders. When extrusion molding, which will bedescribed later, is performed as in the present invention, moldabilityis improved by adding these binders and a lubricant (for example,graphite or a silane coupling agent), a surface-active agent, ormolybdenum disulfide at a rate ranging from 0.5% by weight to 5% byweight. The amount of binders contained in the gas generatingcomposition of this embodiment is preferably from 0.1% by weight to 15%by weight, more preferably from 0.5% by weight to 10% by weight,particularly preferably from 1% by weight to 5% by weight. If the amountof binders contained therein exceeds this range, the combustion ratewill be lowered, and the number of moles of a gas generated will belowered. Therefore, there is a fear that a function for cushioning thevehicle occupants cannot be satisfactorily fulfilled. If the amount ofbinders contained therein is below this range, there is a fear thatenvironmental resistance performance will be lowered.

A combustion adjusting agent can be further used as an additive in thisembodiment. A substance capable of adjusting the combustion of a gasgenerating agent is recommended as the combustion adjusting agent usableherein. Metallic oxide, such as iron oxide, nickel oxide, copper oxide,zinc oxide, manganese oxide, chrome oxide, cobalt oxide, molybdenumoxide, vanadium oxide, or tungsten oxide; metallic hydroxide, such ascopper hydroxide, cobalt hydroxide, zinc hydroxide, or aluminumhydroxide; and a carbon-based substance, such as active carbon powder,graphite, or carbon black, can be mentioned as specific ones. The amountof the combustion adjusting agent contained in the gas generatingcomposition center is preferably from 0 to 10% by weight, morepreferably from 0 to 5% by weight.

Next, a description will be given of concrete examples of a preferredcombination in this embodiment. It is preferable to use a gas generatingagent in which the above-mentioned nitrogen-containing organic compoundconsists of any one kind of guanidine nitrate, nitroguanidine, and5-aminotetrazole, in which the above-mentioned oxidizing agent consistsof any one kind of or a combination of two or more kinds of strontiumnitrate, basic copper nitrate, phase-stabilized ammonium nitrate,potassium nitrate, and ammonium perchlorate, in which theabove-mentioned slag forming agent consists of any one kind of silica,acid clay, and silicon nitride, and in which the above-mentioned binderconsists of any one kind of or a combination of two or more kinds ofhydroxypropyl methylcellulose, poly vinylpyrrolidone, andpolyacrylamide. Preferably, the nitrogen-containing organic compoundcontains guanidine nitrate ranging from 32.5% by weight to 60% byweight, the oxidizing agent contains strontium nitrate or basic coppernitrate ranging from 35% by weight to 65% by weight, the slag formingagent contains acid clay ranging from 0.5% by weight to 15% by weight,and the binder contains any one kind of polyacrylamide, hydroxypropylmethylcellulose, and poly vinylpyrrolidone ranging from 0.5% by weightto 15% by weight. Preferably, the non-azide-based composition usable inthis embodiment contains a nitrogen-containing organic compound rangingfrom 32.5% by weight to 60% by weight, an oxidizing agent ranging from35% by weight to 65% by weight, a slag forming agent ranging from 0.5%by weight to 15% by weight, and a binder ranging from 0.5% by weight to15% by weight. Preferably, the non-azide-based composition containsguanidine nitrate for the nitrogen-containing organic compound andcontains at least two kinds selected from the group consisting ofstrontium nitrate, basic copper nitrate, and phase-stabilized ammoniumnitrate for the oxidizing agent. In more detail, preferred combinationsare as follows.

-   (1) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight    (preferably, from 12% by weight to 30% by weight)-   Additive: residue (preferably, from 0.5% by weight to 15% by weight)-   (2) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight-   Phase-stabilized ammonium nitrate: from 1% by weight to 30% by    weight-   Additive: residue (preferably, from 0.5% by weight to 15% by weight)

Preferably, a combination of a silane coupling agent and synthetichydrotalcite, a combination of a binder for extrusion molding and alubricant, or acid clay is used as the additive. Preferred combinationsusing these are as follows.

-   (1) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight-   Acid clay: from 0.5% by weight to 15% by weight-   Polyacrylamide: from 0.5% by weight to 15% by weight-   (2) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight-   Acid clay: from 0.5% by weight to 15% by weight-   Hydroxypropyl methylcellulose: from 0.5% by weight to 15% by weight-   (3) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight    (preferably, from 1% by weight to 20% by weight)-   Phase-stabilized ammonium nitrate: from 1% by weight to 30% by    weight-   Acid clay: from 0.5% by weight to 15% by weight-   Poly vinylpyrrolidone: from 0.5% by weight to 15% by weight-   (4) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight-   Binder for extrusion molding: from 0.5% by weight to 15% by weight-   Lubricant: from 0% by weight to 5% by weight-   (5) Guanidine nitrate: from 32.5% by weight to 60% by weight-   Strontium nitrate: from 12% by weight to 50% by weight-   Basic copper nitrate: from 1% by weight to 30% by weight-   Binder: from 0.5% by weight to 15% by weight-   Acid clay: from 1% by weight to 5% by weight-   Graphite: from 0.2% by weight to 5% by weight

Normally, time taken from the ignition of the gas generating agent ofthis embodiment to start-up ranges from 1.0 ms to 5.0 ms, preferablyfrom 1.7 ms to 5.0 ms.

Next, a description will be given of an example of a process forproducing the gas generating agent of this embodiment. First, thenon-azide-based composition composed of the above-mentionednitrogen-containing organic compound, the oxidizing agent, the slagforming agent, the binder, etc., is mixed by use of a V-type mixer, arocking mixer, or a ball mill. A silane coupling agent proper inquantity is then added to the composition, and is mixed while addingwater or a solvent (for example, ethanol). As a result, a wet mixturepressed into a lump is obtained. Herein, the “wet” state means a stateof having plasticity to some degree and containing water or a solvent ofpreferably from 10% to 25%, more preferably from 13% to 18%. It ispermissible to pre-mix the silane coupling agent with water or a solventand then add the resulting mixture. At this time, a chemical linkageoccurs among the nitrogen-containing organic compound, the oxidizingagent, and the silane coupling agent, and a bonding force thereamong israised. After that, the wet mixture pressed into a lump is put into anextrusion molding machine (for example, a molding machine provided witha die and a pin for an inside hole at its outlet) without any change forextrusion molding, and is molded into a hollow cylindrical moldedarticle whose outer diameter D is preferably from 1.4 mm to 4 mm, morepreferably from 1.5 mm to 3.5 mm and whose spatial inner diameter d ispreferably from 0.3 mm to 1.2 mm, more preferably from 0.5 mm to 1.2 mm.

Thereafter, as shown in FIG. 1, the hollow cylindrical molded articleextruded from the extrusion molding machine 8 is sent between a pair ofmolding gears 3 and 4 without being dried in air while being drawn bymeans of a drawing belt 2 of a rotary cutter 1 shown in FIG. 1. Themolding gears 3 and 4 are rotated in mutually opposite directions so asto push the molded article S downward and are rotated so that convexteeth formed on the surfaces of the gears 3 and 4 face each other, thusforming the molded article S having squashed-parts at equal intervals.Accordingly, the resulting molded article S is squashed at equalintervals.

As shown in FIG. 2(a), the molding gear 3 (4) has convex teeth 5 (5′)arranged at equal intervals on its surface. As shown in FIG. 3, which isan enlarged view of “A” part in FIG. 2(a), each convex tooth 5 is formedto be thin and acute so that squashed parts of the molded article Sbecome small.

As shown in FIG. 4, the molding gears 3 and 4 are disposed so that aslight gap is created between the molding gears 3 and 4 in a state inwhich the convex teeth 5 and 5′ formed on the surfaces of the moldinggears 3 and 4 are butted against each other. This makes it possible toform a squashed concave part 12 while holding a space 6 inside withoutallowing the molded article S to be cut off by the molding gears 3 and 4when the molded article S passes through the gap between the moldinggears 3 and 4. One condition for forming the squashed concave part 12without being cut off as shown in FIG. 4 is to pass the molded articleS, which is soft, between the molding gears 3 and 4 without drying themolded article S, which has undergone extrusion molding, in air.

After being cut off in such a way as to be folded at each squashedconcave part 12, the molded article S is dried through two stages, i.e.,is dried normally at a temperature of 50° C. to 60° C. for 4 to 10 hoursand is then dried normally at a temperature of 105° C. to 120° C. for 6to 10 hours. As a result, a tubular gas-generating agent 10 whoseinterior has a space 6 in a state in which an end part 7 has beensquashed can be obtained as shown in FIG. 5.

Such a gas generating agent 10 can be obtained by another method. Indetail, the resulting molded article S is dried through two stages,i.e., is dried preferably at a temperature of 50° C. to 60° C. for 4 to10 hours and is then dried preferably at a temperature of 105° C. to120° C. for 6 to 10 hours. After being dried, a ball used to fold themolded article S is put into a V-type mixer, a ball mill, or a rockingmixer together with the molded article S, and these are mixed for 3 to60 minutes so as to fold the molded article S. The ball mentioned hereto fold the molded article S is a metal, such as iron, that has aspecific gravity of 1.0 to 8.0 and that is covered with Teflon or resin.After being cut off in such a way as to be folded at each squashedconcave part 12, classification is performed. As a result, a tubular gasgenerating agent 10 whose interior has a space 6 in a state in which anend part 7 has been squashed can be obtained as shown in FIG. 5.

Preferably, the gas generating agent 10 has a length of 1.5 mm to 8 mm.The fracture surface of the end part 7 is roughened by being cut off insuch a way as to be folded. As a result, a larger surface area can beobtained, and inflammability is improved, and therefore ignitability isimproved. If the molded article S is directly dried at a temperature of105° C. to 120° C., there arises the fear that its shape will beaffected so as to be warped or bent. Therefore, in order to graduallystabilize the shape, it is preferable to dry the molded article S at alow temperature at a first stage and dry it at a high temperature at asubsequent stage. In the gas generating agent 10 molded so as to squashboth ends thereof, the squashed part is thinner than the thickness ofthe gas generating agent 10, and the squashed part is first burnt out,and therefore the gas generating agent 10 is burnt in a state in whichboth ends thereof are opened.

Since the gas generating agent 10 is molded so as to squash both endsthereof in this way, the squashed part of the end part 7 is gently burntimmediately after ignition, and then the gas generating agent 10 israpidly burnt from the outer surface of the tube part and from the innersurface of the internal space 6. Therefore, a pressure-time curve istraced like the letter S, and the gas generating agent 10 is suitable asa gas generating agent used in an air-bag gas generator.

Additionally, since both ends thereof are squashed, the compressionstrength thereof is higher than that of a conventional single-holetubular agent. Therefore, when the gas generating agent 10 is mounted inthe vehicle as a gas generating agent at the time of the generation ofgas, the gas generating agent 10 is superior in resistance to vibration,and a change in shape with the passage of time can be controlled.

Additionally, since the gas generating agent 10 of the present inventionis higher in compression strength than the conventional single-holetubular agent as mentioned above and since both end parts thereof aresquashed to exhibit roundness, the gas generator can be filled with thegas generating agent 10 with a high filling density, and therefore thegas generator can be reduced in size and weight.

A gas generator for a device for protecting vehicle occupants, such asan air bag, that uses the gas generating agent of this embodiment canexhibit a preferred gas generation performance.

The present embodiment will be described according to the followingexamples. It is to be noted that the present embodiment is not limitedto the following examples.

EXAMPLE 1

3% by weight ethanol and 13% by weight water were added to a compositionmixed by a combination of 43.5% by weight guanidine nitrate, 25% byweight strontium nitrate, 25% by weight basic copper nitrate, 2.5% byweight acid clay, and 4% by weight polyacrylamide, and these were mixedand kneaded together to form a kneaded mass. The kneaded mass wasextruded with an extrusion pressure of 8 MPa by means of an extrudingmachine provided with a die having an inner diameter of 2 mm and aninner-hole pin having an outer diameter of 0.5 mm at its outlet. Aresulting molded article shaped like an extruding rod was sent betweenmolding gears while being drawn by a drawing belt. The molded articlewas formed to have concave parts with intervals of 4.4 mm by means ofconvex teeth of the molding gears. The molded article was cut off insuch a way as to be folded at the concave parts, and was then dried at atemperature of 55° C. for 8 hours, and was then dried at a temperatureof 110° C. for 8 hours. As a result, a gas generating agent wasobtained.

EXAMPLE 2

The above-mentioned substances were mixed and kneaded in the same way asin Example 1. Thereafter, the kneaded mass was extruded with anextrusion pressure of 8 MPa by means of an extruding machine providedwith a die having an inner diameter of 2 mm and an inner-hole pin havingan outer diameter of 0.8 mm at its outlet. A resulting molded articleshaped like an extruding rod was sent between molding gears while beingdrawn by a drawing belt. The molded article was formed to have concaveparts with intervals of 4.4 mm by means of convex teeth of the moldinggears. The molded article was cut off in such a way as to be folded atthe concave parts, and was then dried at a temperature of 55° C. for 8hours, and was then dried at a temperature of 110° C. for 8 hours. As aresult, a gas generating agent was obtained.

EXAMPLE 3

3% by weight ethanol and 13% by weight water were added to a compositionmixed by a combination of 40.6% by weight guanidine nitrate, 25% byweight strontium nitrate, 25% by weight basic copper nitrate, 4.8% byweight acid clay, 2.3% by weight hydroxypropyl methylcellulose, 1.6% byweight polyvinylpyrrolidone, 0.5% by weight graphite, and 0.2% by weightsilicon dioxide were mixed and kneaded together to form a kneaded mass.The kneaded mass was extruded with an extrusion pressure of 10 MPa bymeans of an extruding machine provided with a die having an innerdiameter of 3 mm and an inner-hole pin having an outer diameter of 1.0mm at its outlet. A resulting molded article shaped like an extrudingrod was sent between molding gears while being drawn by a drawing belt.The molded article was formed to have concave parts with intervals of4.4 mm by means of convex teeth of the molding gears. The molded articlewas dried at a temperature of 55° C. for 8 hours, and was then dried ata temperature of 110° C. for 8 hours. The molded article was cut off insuch a way as to be folded at the squashed concave parts, and thenclassification was performed. As a result, a gas generating agent wasobtained.

COMPARATIVE EXAMPLE 1

A molded article shaped like the extruding rod was molded in the sameway as in Example 1. Thereafter, the molded article was drawn by thedrawing belt and was dried in air. The molded article, which has reachedthe state of not being squashed, was cut off, and was dried at atemperature of 55° C. for 8 hours, and was then dried at a temperatureof 110° C. for 8 hours. As a result, a gas generating agent wasobtained.

COMPARATIVE EXAMPLE 2

A molded article shaped like the extruding rod was molded in the sameway as in Example 2. Thereafter, the molded article was drawn by thedrawing belt and was dried in air. The molded article, which has reachedthe state of not being squashed, was cut off, and was dried at atemperature of 55° C. for 8 hours, and was then dried at a temperatureof 110° C. for 8 hours. As a result, a gas generating agent wasobtained.

FIG. 7 and FIG. 6 show characteristics of the gas generating agents ofExamples 1 and 2 and Comparative examples 1 and 2 mentioned above andresults of tank combustion tests.

The tank combustion tests in FIG. 7 were conducted as follows. Astainless steel tank container whose internal volume is 60 liters wasfilled with each gas generating agent of Examples 1 and 2 andComparative examples 1 and 2. A gas generator provided with an ignitiondevice was attached thereto, and the gas generating agent placed in thetank container was burnt by outside ignition. The internal pressure ofthe tank container on a time base was measured by a piezoelectricelement disposed in the tank container.

As is understood from FIG. 7 and FIG. 6, the pressure-time curve istraced like the letter S in Examples 1 and 2 and in Comparative examples1 and 2 according to this embodiment. However, the gas generating agentmolded so that both ends thereof are squashed as in Examples 1 and 2according to the present invention is characterized in that time fromignition to start-up and time from the start-up to the attainment of atank maximum pressure are longer than those of the corresponding gasgenerating agents of Comparative examples 1 and 2. Therefore, the gasgenerating agents of Examples 1 and 2 according to the present inventionare burnt more gently than the corresponding gas generating agents ofComparative examples 1 and 2. Thus, it has been understood that the gasgenerating agent according to the present invention can moderate amechanical shock caused by rapid inflation of an air bag at thebeginning of air-bag expansion.

Although the present invention was described with reference to theabove-mentioned preferred embodiment, the present invention is notlimited to this. It will be understood that various embodiments notdeparting from the spirit and scope of the present invention can becarried out.

1. A gas generating agent wherein the gas generating agent is a tubularmolded article formed with a non-azide-based composition, and both endsof the molded article are squashed.
 2. The gas generating agent asrecited in claim 1, wherein an outer diameter D of the molded article ofthe gas generating agent is from 1.4 mm to 4 mm, a length L thereof isfrom 1.5 mm to 8 mm, and an inner diameter d of an internal space of themolded article is from 0.3 mm to 1.2 mm.
 3. The gas generating agent asrecited in claim 1 or claim 2, wherein a tank maximum pressure P (kPa)is from 50 kPa to 700 kPa in a tank combustion test.
 4. The gasgenerating agent as recited in claim 1 or claim 2, wherein time T (ms)from the start-up of a tank pressure to the attainment of a tank maximumpressure P (kPa) is from 20 ms to 100 ms, and a pressure-time curve istraced like the letter S.
 5. The gas generating agent as recited inclaim 1 or claim 2, wherein the non-azide-based composition is composedof a nitrogen-containing organic compound, an oxidizing agent, a slagforming agent, and a binder.
 6. The gas generating agent as recited inclaim 5, wherein the non-azide-based composition has a combination ofthe nitrogen-containing organic compound ranging from 32.5% by weight to60% by weight, the oxidizing agent ranging from 35% by weight to 65% byweight, the slag forming agent ranging from 0.5% by weight to 15% byweight, and the binder ranging from 0.5% by weight to 15% by weight. 7.The gas generating agent as recited in claim 5, wherein thenitrogen-containing organic compound is one kind or two or more kindsselected from the group consisting of a tetrazole derivative and aguanidine derivative.
 8. The gas generating agent as recited in claim 5,wherein the nitrogen-containing organic compound consists of any onekind of guanidine nitrate, nitroguanidine, and 5-aminotetrazole; theoxidizing agent consists of any one kind of or a combination of two ormore kinds of strontium nitrate, basic copper nitrate, phase-stabilizedammonium nitrate, potassium nitrate, and ammonium perchlorate; the slagforming agent consists of any one kind of silica, acid clay, and siliconnitride; and the binder consists of any one kind of or a combination oftwo or more kinds of hydroxypropyl methylcellulose,polyvinylpyrrolidone, and polyacrylamide.
 9. The gas generating agent asrecited in claim 8, wherein the nitrogen-containing organic compoundcontains guanidine nitrate ranging from 32.5% by weight to 60% byweight; the oxidizing agent contains strontium nitrate or basic coppernitrate ranging from 35% by weight to 65% by weight; the slag formingagent contains acid clay ranging from 0.5% by weight to 15% by weight;and the binder contains any one kind of polyacrylamide, hydroxypropylmethylcellulose, polyvinylpyrrolidone, graphite, and silicon dioxideranging from 0.5% by weight to 15% by weight.
 10. A process forproducing a gas generating agent tubularly molded so as to squash bothends thereof, comprising the steps of passing a tubular molded articleof a gas generating agent being wet through a gap between a pair ofmolding gears rotated so that mutual convex teeth of the molding gearsface each other; squashing the molded article at predetermined intervalsby means of the convex teeth; and cutting the molded article in such away as to fold the molded article at squashed concave parts thereof anddrying resultant pieces.
 11. A process for producing a gas generatingagent, comprising the steps of passing a tubular molded article of a gasgenerating agent being wet through a gap between a pair of molding gearsrotated so that mutual convex teeth of the molding gears face eachother; squashing the molded article at predetermined intervals by meansof the convex teeth; drying the molded article; and cutting the moldedarticle.
 12. A process for producing the gas generating agent of claim11 wherein both ends thereof are squashed.
 13. A process for producingthe gas generating agent of claim 11 or claim 12 wherein the moldedarticle is cut in such a way as to be folded at squashed concave parts,and then classification is performed.
 14. An air-bag gas generator usingthe gas generating agent of claim
 1. 15. An air-bag gas generator usingthe gas generating agent of claim
 2. 16. An air-bag gas generator usingthe gas generating agent of claim
 3. 17. An air-bag gas generator usingthe gas generating agent of claim
 4. 18. An air-bag gas generator usingthe gas generating agent of claim
 5. 19. An air-bag gas generator usingthe gas generating agent of claim
 6. 20. An air-bag gas generator usingthe gas generating agent of claim
 7. 21. An air-bag gas generator usingthe gas generating agent of claim
 8. 22. An air-bag gas generator usingthe gas generating agent of claim 9.